Meetings

Issue 20, Winter 1997

NSIDC has begun the development of the Antarctic Data Coordination Center (ADCC) at NSIDC. The ADCC will provide a U.S. focus for the collection of metadata for the Antarctic Master Directory (AMD) which is being hosted at the International Center for Antarctic Information and Research (ICAIR) in Christchurch, New Zealand. The National Science Foundation's (NSF) Office of Polar Programs is funding the ADCC activity at NSIDC and much of the AMD effort at ICAIR. The AMD will be closely linked to the NASA Global Change Master Directory.

NSIDC will identify Antarctic data sets (and cognizant individuals for these data sets) in all disciplines and prepare or assist in the preparation of data descriptions (DIFs) which will be the basis of the AMD. Already underway is an inventory of U.S. Antarctic data sites on the World Wide Web. We also have prepared a brochure for the ADCC. Recently, NSIDC briefed the National Research Council/National Academy of Sciences Polar Research Board on this activity. The Board provided much of the impetus for the coordination of metadata for the Antarctic through its involvement in the Scientific Committee for Antarctic Research (SCAR). NSIDC also met with the relevant program managers from NSF to review plans for the ADCC.

On January 14, Vice President Gore announced a new atlas of Arctic oceanographic information in a press conference at the National Geographic Society. NSIDC is distributing this atlas. More than 1.3 million individual temperature and salinity observations on the Arctic Ocean collected over the period 1948-1993 from Russian drifting stations, ice breakers, and airborne expeditions were used to develop the atlas. Approximately 70% of the observations for the Arctic Ocean and shelf seas in this atlas are derived from Russian archives of formerly restricted data with 30% from comparable sources in the U.S. An article about the data in the February issue of National Geographic ("Arctic Breakthrough", volume 191(2), p. 36-57) describes, in a forward by Vice President Gore, the negotiations with Russian Prime Minister Viktor Chernomyrdin that led to the release of the data. The news story was immediately picked up by the wire services and on the next day it appeared in newspapers and news services on the Web. Within 24 hours of the announcement, NSIDC had 50 orders for the CD-ROM. At this writing, orders have topped 300.

The atlas is the result of the work of the Gore-Chernomyrdin Commission's Environmental Working Group (EWG) Subgroup on Arctic Climatology. Russian Minister V.I. Danilov-Danilyan and NOAA Director Dr. James Baker co-chair the EWG. The CD-ROM itself was put together by the Environmental Research Institute of Michigan, with the assist of scientists in the Subgroup on Arctic Climatology. Professor Norbert Untersteiner, chair of the Department of Atmospheric Sciences at the University of Washington, is one of the principals in this group. The atlas, the full title of which is Environmental Working Group Joint U.S.-Russian Atlas of the Arctic Ocean, Oceanography Atlas for the Winter Period, is the first in a series. Later volumes will be a summer oceanography atlas, an arctic meteorology atlas, and an arctic sea ice atlas. NSIDC is directly involved in the development of the meteorology and sea ice atlases. These will be released through 1997 and 1998.

PRODUCTS AND SERVICES

The AARI 10-Day Arctic Ocean EASE-Grid Sea Ice Observations data set is now available and will replace the AARI 10-Day Digital Arctic Sea Ice Charts in the NSIDC Data Catalog. The data set originated with operational ice charts compiled by the Arctic and Antarctic Research Institute (AARI) in St. Petersburg, Russia. Coverage dates from 1953 to 1990, and the data set consists of total ice concentration as well as concentration by stage of development (multi-year ice, first year ice, younger ice, and fast ice). Generally, there is a chart every 10 days.

The operational charts were encoded in Sea IceGrid (SIGRID) format, and transferred from AARI to NSIDC as part of a NOAA-funded data rescue effort through the World Meteorological Organization's Global Digital Sea Ice Data Bank (GDSIDB) project. The steering group for GDSIDB uses SIGRID because of its acceptance by the operational community as a standard format for digitally encoding paper chart data. However, using a SIGRID- coded chart for a climatological study would be difficult for several reasons. First, the Sea Ice Grid is of variable size depending on longitude. Secondly, software tools must be written to parse the alphanumeric code and present it for analysis as recognizable ice information. Finally, a SIGRID file is 10 layers deep, with one layer for total ice concentration, and other layers for the concentration, stage of development, and form of the first, second and third thickest ice. While the information on stage of development is richly detailed, several steps would be required before a user interested in ice mass balance, for example, could determine the concentration of multi-year ice in a given area.

To make the data easier to use, the SIGRID files were transformed to the NSIDC EASE-Grid, using a 12.5-km resolution grid on an azimuthal, equal-area projection. EASE-Grid is used for Polar Pathfinder products, including SSM/I Brightness Temperatures and AVHRR products. Having ice concentrations by type in EASE- Grid makes it easy to ascertain quickly the concentration of a certain ice type in a certain area.

The AARI data do not cover the same areas with constant sampling intervals in every year. The data were acquired to assist shipping in the Northern Sea Route, so the observations tend to be at lower latitudes and more prevalent in the summer months, especially in the early part of the data set. For instance, 1953 has a total of 11 charts, six for the eastern sector and five for the western sector, beginning in March and ending in September, while 1987 has 31 files for the eastern sector and 36 for the western sector, beginning in January and ending in December. This has not hindered us from making a preliminary study comparing monthly average SSM/I and SMMR ice concentrations with AARI data from 1978 to 1991. We found that AARI data show more open water (about 20 percent more on average) while the passive microwave data have more ice that falls in the intermediate concentration range of 16 to 79 percent. This seems largely attributable to the relatively low resolution of passive microwave data. Small open water areas such as flaw leads and polynyas that are defined in the AARI data set often appear as larger areas of intermediate concentration in the passive microwave data. The ice edge is also much more abrupt in the AARI data.

The National Snow and Ice Data Center has developed a northern hemisphere cryospheric product which combines snow cover and sea ice extent at weekly intervals for the period 1978 to 1995 (snow cover extent data alone are available from 1971). The data set also includes monthly climatologies describing snow and sea ice extent in terms of average conditions, probability of occurrence, and variance. The data set is produced in an azimuthal equal area (25 km) projection (NSIDC EASE-Grid) and is available on two CD-ROMs. The snow cover extent is based on the digital NOAA-NESDIS weekly northern hemisphere snow charts, revised by D. Robinson (Rutgers University) and re-gridded to the EASE-Grid. The original NOAA-NESDIS weekly snow charts are derived from the manual interpretation of AVHRR, GOES and other visible-band satellite data. The sea ice extent is based on the existing NSIDC, polar stereographic, sea ice concentration grids. The NSIDC sea ice concentrations are derived from the SMMR and SSM/I passive microwave brightness temperature data. Funding for this project has been provided by the NOAA Climate and Global Change Program and the NASA Pathfinder Program.

The Former Soviet Union (FSU) Hydrological Snow Survey data are now available from NSIDC. The development of this data set was funded by NOAA's Environmental Services, Data, and Information Management (ESDIM) project through the National Geophysical Data Center (NGDC).

The FSU Hydrological Snow Surveys are based upon observations made by personnel at 1345 sites throughout the Former Soviet Union. These observations include snow depths at World Meteorological Organization stations and snow depth and snow water equivalent measured over a nearby snow course transect on a single day. The station snow depth measurements are a ten-day average of individual snow depth measurements. The transect snow depth data are the spatial average of 100 to 200 individual measuring points. The transect snow water equivalent is the spatial average of twenty individual measuring points. Data, covering 1966 through the end of 1990, were acquired from the Institute of Geography, Russian Academy of Sciences, Moscow, where they were digitized under the supervision of Professor Alexander Krenke.

A complete description of the FSU Hydrological Snow Survey data is available in NSIDC's Data Catalog. The data are accessible through an interface which allows the user to extract data based upon simple geographic searches or by the day or month.

DMSP F13 SSM/I Daily and Monthly Polar Gridded Sea Ice Concentrations are available via ftp, with plans underway to produce the data on CD-ROM. The data are derived from the brightness temperature grids produced and distributed by NSIDC, and are processed from May 1995 through March 1996. Updates to the data set will be staged to the ftp site as they become available. Data may be accessed by ftp.

NSIDC staff have redesigned the Data Center's World Wide Web site, expanding the gallery, improving the educational offerings, and reorganizing the NSIDC Data Catalog. Users can now locate approximately 100 of our cryospheric data sets by subject, title, project, or funding agency. Complete documentation is readily available for all of these data sets, and many data sets are directly available via ftp.

The redesigned data catalog includes access tools for the Eurasian Glacier Inventory and the Former Soviet Union Hydrological Snow Surveys. A browse tool for the Polar 1-Km Advanced Very High Resolution Radiometer data set is in development, and a snow glossary, a snow fact sheet, and a list of questions and answers about snow are planned.

New pages evolve daily, so please browse the new NSIDC web site and let us know what you think.

The EOS Moderate Resolution Imaging Spectroradiometer (MODIS) Instrument Team has announced the planned availability of a sea ice surface temperature (IST) product beginning with the launch of the EOS AM-1 satellite in June 1998. NSIDC will archive and distribute the suite of MODIS snow and ice products being developed by Drs. Vince Salomonson and Dorothy Hall of the MODIS Team. The IST algorithm, which is based on work by Key and Haefliger (1992) and the POLES IDS Team using AVHRR and Landsat TM data, will be used in conjunction with the ICEMAP sea ice extent algorithm and the MODIS cloud mask to produce daily global sea ice indices at 1-km resolution.

Sea Ice Data Sets

NSIDC distributes a variety of sea ice data products. This article describes the general characteristics of the major sea ice data sets, so that users may select the products most appropriate for their applications.

Passive microwave derived daily sea ice concentrations are available from the SMMR and SSM/I sensors for both polar regions beginning in October 1978 and on-going. The data are derived from SMMR and SSM/I brightness temperatures and are provided in a 25-km polar stereographic grid. In addition, there is a monthly gridded product from 1987 that is also ongoing. Data from 1978 through 1991 are available on CD-ROM, and data from 1991 are available via anonymous ftp with plans for CD-ROM production underway.

The CD-ROM Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent, combines snow cover and sea ice extent at weekly intervals for October 1978 through August 1995, and snow cover alone for January 1971 through October 1978. See Northern Hemisphere EASE-Grid Weekly Snow Cover and Sea Ice Extent for further information on this data set.

Data sets in this category are derived from a variety of sources including AVHRR, DMSP OLS and SSM/I, aerial reconnaissance, and ship and station observations.

Specific data sets in this category include the National Ice Center Arctic and Antarctic Sea Ice Data 1972- 1994 on CD-ROM. Data are digitized and stored in SIGRID, the WMO standard exchange format for digitized sea ice charts. NSIDC plans to reprocess the data into the NSIDC EASE-Grid. Look for the announcement of availability in future issues of NSIDC Notes.

The AARI 10-Day Arctic Ocean EASE-Grid Sea Ice Observations, also originally in the SIGRID format, have been reprocessed into the NSIDC EASE-Grid and are available now. See p. 1, "New Russian. . .," for further details.

National Meteorological Center/Climate Analysis Center Arctic and Antarctic Sea Ice, 1973-1990, gives the extent of sea ice at the end of each month for thirty-six, 10°longitude sectors in each hemisphere. Ice extent is digitized from the U.S. National Ice Center charts.

Arctic and Southern Ocean Sea Ice Concentration Data range from 1901 through 1995 for the Arctic, and from 1973 through 1995 for the Southern Ocean data. The data sources are U.S. Fleet Weather Facility, U.S. National Ice Center, U.S. Naval Oceanographic Office, Canadian Department of Transport, British Meteorological Office, Danish Meteorological Institute, Norwegian Polar Institute, and Icelandic ice summaries. The data were produced by Dr. John E. Walsh and Bill Chapman, University of Illinois, and intended for use in hemispheric-scale modeling. Arctic data for 1901-1953 were compiled by Dr. P.M. Kelly, University of East Anglia.

NSIDC also archives a number of smaller project and campaign-related data sets. For more information on NSIDC products and services, please contact NSIDC User Services. You can also view our Data Catalog.

NEWS FROM OTHER CENTERS

ERS-1's scatterometer, the AMI in Wind Mode, has regularly covered both polar oceans from August 1991 to May 1996, and the quality of its backscatter measurements, confirmed by an on-going calibration activity, makes it well adapted to monitor sea ice extent and distinguish ice types.

The Institut Français de Recherche pour l'Exploration de la Mer (IFREMER) Department of Oceanography from Space has produced a CD-ROM containing maps of three variables: the backscatter coefficient at 40° and 50° incidence angle and its derivative at 28°, as well as an ice mask determined from the Maximum Likelihood Estimator, normalized distance from the measured backscatter triplets to a wind- over-water backscatter model. The three variables are computed from the initial backscatter measurements which extend over an incidence angle range of 18° to 58°. Weekly maps in the NSIDC 25-km polar projections of these variables are recorded on the CD-ROM and can be extracted as numerical data using the software provided.

Browsing through the images on the CD-ROM, from week to week or from year to year, is done simply, using NETSCAPE or MOSAIC, but the images can also be read in different image formats including GIF. Moreover, six examples of simple applications are given, amongst which ice drift in the Arctic Ocean and maximum extent of sea ice in the Antarctic Ocean, are particularly illustrative. Thus the data set can serve experienced oceanographers who are already using SSM/I products provided by NSIDC and looking for complementary backscatter data, as well as teachers and students in climatology or oceanography, who want a rapid introduction to sea ice dynamics and remote sensing.

MEETINGS

The primary goal of the workshop is to bring together the terrestrial and planetary science communities whose focus is remotely sensed surface ice research. The workshop will address issues such as the current problems and objectives in surface ice studies, methods and technologies currently employed, and future requirements for instrumentation, field studies, supporting laboratory measurements and theoretical modelling. The intent is that collaboration between the two communities can be developed and deepened to take advantage of joint programs and decrease redundancies in a fiscally tight era.

Potential Topics include:

Observation and analysis of ices in the visible, near-infrared, thermal infrared, or microwave regions using imaging, spectroscopy, photometry, or SAR